1. Field of the Invention
The present invention relates to a miniature pump that can be used in a cooling system or the like. It relates in particular to a miniature pump with improved stable-discharge characteristics. Furthermore, the present invention relates to a cooling system and portable equipment using such a miniature pump.
2. Description of Related Art
In conventional diaphragm type miniature pumps, their sizes have been reduced considerably by adopting a vibrating plate made of a piezoelectric element, for example, PZT. FIG. 18 shows an example thereof.
In this figure, numeral 300 denotes a piezoelectric vibrating plate including a piezoelectric substrate 310 and a vibrating plate 320, numeral 330 denotes suction and exhaust valves for controlling a liquid flow, and numeral 340 denotes a casing forming a pressure chamber 500 and a flow passage. The piezoelectric substrate 310 is attached to the vibrating plate 320 so as to form the piezoelectric vibrating plate 300 serving as a diaphragm. An AC voltage is applied to the piezoelectric substrate 310 of this piezoelectric vibrating plate 300, thereby concaving or convexing the piezoelectric vibrating plate 300. The resulting change in volume of the pressure chamber 500 and the resulting movement of the valves 330 bring about a pumping function.
Next, the movement of the valves and that of the piezoelectric vibrating plate during suction and exhaustion will be described more specifically referring to FIGS. 19A and 19B. In these figures, arrows 10 indicate a liquid flow direction.
FIG. 19A shows a sucking operation of the miniature pump, and FIG. 19B shows a discharging operation thereof. As shown in these figures, an AC voltage is applied to the piezoelectric vibrating plate 300 so as to deform it toward the direction that increases the volume of the pressure chamber 500, thereby sucking a fluid through a suction valve 330a into the pressure chamber 500 (see FIG. 19A). Also, the application of an AC voltage causes the piezoelectric vibrating plate 300 to deform in the direction that decreases the volume of the pressure chamber 500, thereby discharging the fluid, which has been sucked into the pressure chamber 500, from a discharge port through an exhaust valve 330b (see FIG. 19B).
However, although the above-described conventional diaphragm type miniature pumps can be made much smaller than those converting a rotational motion of a motor into a reciprocating motion using a motion converter so as to drive a diaphragm, it is difficult to increase the area of the diaphragm. Accordingly, when it comes to a pumping performance, the discharge flow rate has been rather small. For example, in the case where a unimorph type piezoelectric vibrating plate with a diameter of 25 mm was used as a driving source and driven at an AC voltage of 100 V rms, only a flow rate of about 30 cm3/min was obtained with respect to 60 Hz driving.
It is an object of the present invention to provide a miniature pump that achieves both a large discharge flow rate and stable discharge flow rate characteristics, and a cooling system and portable equipment using this miniature pump.
In order to achieve the above-mentioned object, a miniature pump of the present invention includes a miniature pump portion including a suction passage through which a liquid flows in, and a discharge passage through which the liquid flows out; and a bubble trap portion for blocking an entry of air bubbles into the miniature pump portion.